In recent years, by forming a semiconductor element over a rigid substrate such as a glass substrate, a semiconductor device has been actively developed for use in a display such as an LCD or an organic EL display, a photoelectric conversion element such as a photo sensor or a solar cell, or the like. Besides, a semiconductor device which transmits and receives data without contact (also referred to as an RFID (Radio Frequency Identification) tag, an ID tag, an IC tag, an IC chip, a wireless tag, an electronic tag, or a wireless chip) has been actively developed. In addition, recently, a flexible device such as a film-state display or a semiconductor device embedded in paper has been required, and a reduction in thickness holds an important clue.
In order to reduce thickness of a semiconductor device, there is a method for using a substrate which is thinned in advance, for example. However, in this case, warpage or the like of the substrate, or, in dealing with the element, warpage due to stress, difficulty in handling, misalignment in lithography or a printing step, and the like become problems. Therefore, a method for thinning or removing a substrate after forming a semiconductor element over the substrate is generally used.
As a method for thinning or removing a substrate, for example, there is a technique for removing a supporting substrate (a glass substrate) by grinding treatment or polishing treatment, or wet etching using a chemical reaction (for example, see Reference 1: Japanese Published Patent Application No. 2002-87844).